This invention relates to a centering mechanism for use with injection mold systems and in particular to a centering mechanism utilizing a threaded rod to connect and maintain proper spacing of mold plates in the injection mold system.
It is well known in the art of injection molding to use opposing faces of adjacent mold plates, one defining a cavity, the other including a mold core which mates with the cavity, creating a cavity therebetween. These plates are brought together and molten plastic is injected between adjacent mating plates. Mold plates are cooled to cause solidification of the plastic. The plates are then separated and the finished plastic article ejected. In order to achieve high volume production, a stack mold is often used, wherein two or more sets of molds are interspersed in sequence in which rows of mold cores and mold cavities (often referred to as mold levels or mold sets) are stacked in a single machine. In conventional stack molds, typically, a central, first mold plate is provided, for holding the mold cavities of the respective stacks of molds. Typically, the central plate comprises two or more abutting plates, and is connected to cooling lines and the like for cooling of the injected molten plastic.
Two outer, second mold plates are located on either side of the central plate, with the entire system opening and closing during the molding process. One of the outer, second mold plates is affixed to a stationary platen of a conventional molding machine, while the other outer mold plate is attached to the moveable platen, so this other outer, second mold plate and the central first mold plate move in the opening and closing process of molding.
For a stack mold to operate properly the mold plates must have equal spacing between them all the time. The prior art reveals various systems for spacing the central first plate (often referred to as the floating hot runner) from the second plates. Once such system comprises a threaded rod carried by a central plate, which engages threaded sleeves carried by second mold plates. These are attached to the peripheries of the respective mold plates, and serve to keep the first, central mold plate centered between the second plates on either side of the central mold.
An example of a mold plate centering system is shown in U.S. Pat. No. 6,106,265 to Von Holdt. The system disclosed in U.S. Pat. No. 6,106,265 comprises a threaded rod having first and second parts each extending oppositely and outwardly from the first central plate toward the respective second plates. The respective threaded rod parts are typically integrally connected at their central ends where they are retained in rotatable relation to the center mold. The threads of the respective threaded rods are of opposite rotational sense to each other, one extending clockwise and the other counterclockwise.
Such a mold plate centering system is typically placed on each side of the mold set to ensure maximum stabilization. Each of the second plates carries an internally threaded sleeve as part of the mold plate centering system, with each threaded rod part occupying at least a portion of a bore within said sleeve in screw-threaded relationship. Thus, as the respective second plates are moved by the moveable mold platen of the stack mold to which mold system is attached, the threaded shafts of each rod part spontaneously rotate, driven by the screw threads of the internally threaded sleeves on the second plates and the degree of movement of both plates and is firmly limited by the number of rotations of the joined, threaded shafts. Thus, the position of the first plate relative to second plates is strictly controlled and constrained, typically to be exactly equidistant between the respective two second plates at all times along the path of motion and in all positions.
For various reasons, such as to perform stack mold maintenance, unexpected stack mold repair, insert changes on the mold, access to the mold plates is often required. With the utilization of mold centering systems such as that described above, access to the mold plates is somewhat restricted. In particular, with such centering systems, opening of the mold is limited to the length of the threaded portion of the rods because if the mold set is opened beyond the length of the threaded portion of the rods, the threaded rods will disengage from the internally threaded sleeves on the second plates due to their axial rotation. If one of the threaded portions of the rod does become disengaged from the sleeves, in order to ensure that the centering system achieves its desired function of keeping the second plates equidistant from the first plate, realigning of the threaded rod portions within the sleeves is required. Any rotation of the rod while one threaded portion is disengaged and the other engaged will cause the rods to be improperly aligned when reengaged. As such, proper realignment tends to be quite tedious and requires significant time to achieve.
It is an object of the invention to provide an improved stack mold centering system which allows easier access to the mold plates than the centering systems disclosed in the prior art, namely without requiring disengagement of the threaded rods from the mold plates.
The present invention provides an injection mold centering apparatus utilizing a threaded rod secured between mold plates. The mold centering apparatus of the present invention allows the stack mold to be fully opened without the rod losing threaded engagement of mold plates. This is achieved by portions of the threaded rod being separable from each other.
According to one aspect of the present invention, there is provided a mold centering apparatus for controlling relative movement between mold plates in a stack mold, the stack mold comprising a first mold plate positioned between a pair of second mold plates. The first mold plate is connected to the second mold plates by the centering apparatus of the invention. The mold plates are movable along a mold axis between an open position and a closed position. The mold plate includes mold faces on opposite sides of said first plate. The second plates are designed for mating with the faces on opposite sides of the first plate such that in the closed position, molten plastic may be injected between the first and second plates, for producing molded plastic products.
The centering apparatus comprises an elongate threaded rod member comprising a central portion, and two oppositely extending, outer portions extending from the central portion parallel to the mold axis toward each of the second plates. The central portion is attached to a peripheral portion of the first plate. The rod member is axially rotatable with respect to the first plate and the rod member is prevented from axial movement relative to said first plate. Each outer portion includes a threaded portion with the threaded portions of each outer portion having the same thread count and pitch but being in opposite orientation to the other. A threaded connector is secured to the periphery of each second plate and each connector defines a threaded bore therein, mating with each respective threaded portion of the rod, so that each second mold plate is connected with the first mold plate by the rod and connector between the open and closed positions along the mold axis.
The portions of the rod rotate as one unit when secured together as the molding apparatus is moved between the open and closed positions. The outer rod threaded portions rotate within each bore an equal an opposite amount thereby equalizing the distances of each second mold plate from the first mold plate as the apparatus is moved between the open and closed positions. At least one outer portion is releasably detachable from the rod central portion, thereby allowing at least one second mold plate to be separated from the first plate along the mold axis beyond the open position and beyond the length of the threaded portions without axial rotation of the rod and thus without the threaded connector losing threaded engagement with the at least one threaded rod portion.
Further features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which: